The Rosetta Stone alone couldn't crack hieroglyphs

The Rosetta Stone let scholars read Egyptian hieroglyphs because it repeats one priestly decree of 196 BC, honouring Ptolemy V, in hieroglyphic, Demotic and Greek, and Greek was still readable. But the stone alone did not crack the code: Jean-François Champollion announced his decipherment in 1822 only after adding a second inscription and the Coptic language.

Script	Who used it	Lines surviving
Hieroglyphic	Priests, for sacred texts	14
Demotic	Everyday Egyptian writing	32
Greek	The Ptolemaic administration	54

The hieroglyphic band at the top is the most damaged part of the slab, so the section scholars most needed is the shortest. None of the three texts is complete, because the corners of the stela are broken away.

Why the stone was not enough

The Rosetta Stone preserves only one royal name in its cartouches, the oval rings around kings’ names: Ptolemy. Thomas Young, working from 1814, linked those signs to the sounds of Ptolemy’s name. A single name, though, cannot prove which sign makes which sound.

The second name came from an obelisk that William Bankes shipped from Philae to his Dorset estate, arriving in 1821. Its base carried a Greek inscription, and its two cartouches held the names Ptolemy and Cleopatra. Bankes circulated lithographs, and copies reached Champollion. Comparing the two names, which share letters such as p, t, o and l, he could test sound values instead of guessing them. Many popular accounts say both names appear on the Rosetta Stone; Cleopatra’s does not.

Champollion’s other advantage was Coptic, the last stage of the Egyptian language, preserved by Egypt’s Christians, which let him hear the language behind the signs. He showed that hieroglyphs mix sound signs with meaning signs, a system unread for some 1,400 years: the last known hieroglyphic inscription, a graffito at Philae, dates to 394 AD.

Champollion never saw the stone itself while decoding it. Like most scholars after its discovery by French soldiers in 1799, he worked from printed copies.